Reptile Adaptations for Life on Land

Reptiles are a class of ectothermic vertebrates that reproduce with internal fertilization and lay amniotic eggs. They have many adaptations for life on land, including dry, water tight skin; lungs; a metabolic rate that slows during dormancy (hibernation); and the ability to regrow lost body parts.

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Like amphibians, lizards can absorb heat by sun bathing or hiding under rocks or bark to conserve energy. They are also good swimmers, using a side-to-side motion similar to that of eels called lateral undulation.

Scaly Skin

The tough, scaly skin of reptiles protects them from injury and loss of water to the air through evaporation. It also provides mechanical protection against rough terrestrial environments, much harsher than those of their aquatic ancestors.

The outer covering of most reptiles is made from hardened plates of keratin, similar to the fingernails of humans and other mammals. Reptilian scales are often arranged in overlapping layers that form a kind of armor. They typically bear no glands and differ in structure from the skin of amphibians and birds and mammals. A thin epidermis surrounds a thicker dermal portion, called the stratum corneum, in which a waxy substance is secreted that provides strength and lubrication. A hinge region connects adjacent epidermal scales. The hinge region may be strengthened by a combination of b- and a-keratin or by bony plates called osteoderms.

These osteoderms can have a variety of shapes and sizes. They are sometimes adorned with pits, grooves, protuberances and spines. They can be color patterned and they may contain sensory receptors. Some scales can also be hollowed out, allowing prey to hide inside.

The scales of some reptiles, such as crocodiles and turtles, are fused into dermal armor called plastron or carapace. Their ridges can form crests and spines, as well as bony plates that are horn-like. In addition to these defensive adaptations, scaly skin provides camouflage and helps regulate body temperature. In many species, scaly skin is shed periodically in flakes. This allows for replacement of worn and dead scales and disposal of parasites.

Thermoregulation

Reptiles and amphibians have developed a remarkable array of strategies to survive in their environments. Their camouflage, for example, allows them to blend seamlessly with their surroundings and thwart predators’ attempts at spotting prey. But some of these adaptations come with costs, such as the need to get rid of excess heat.

Because they have thin skin and use no internal sources of energy to fuel their metabolisms, most reptiles are ectothermic (relying on external sources of body heat). They regulate their temperature by moving between thermally different environments, such as basking in sunny spots or finding cool or shady places to hide. Some reptiles also brumate, which is the process of using the energy produced by movement to warm the body.

In addition, a number of reptiles have adapted to warm or cool their bodies with the surrounding environment by changing the rates at which they transfer heat to and from the outside. This is known as behavioral thermoregulation. For example, lizards sunbathe and pant to cool themselves; turtles have keratinized shells to protect them from predators and cold water temperatures; and crocodiles chomp on their prey to warm up.

Point out to students that there are two kinds of animal adaptations: physical and behavioral. A polar bear’s thick fur is a physical adaptation; a crocodile’s “playing dead” is a behavioral adaptation.

The Lungs

Reptiles, including snakes, lizards and turtles, have adapted to land and aquatic environments in a wide range of ways. Their thick scaly skin helps conserve moisture inside, and their sprawling gait conserves energy to allow them to rest more easily. They also tend to have efficient excretory systems that help them concentrate waste into firm feces and urine.

While mammals, amphibians and birds have lungs that extract oxygen from the air, most reptiles, including snakes, have trachea-like lungs that absorb gases from the surrounding air. A trachea is a tube-like structure that extends from the larynx to the lungs.

A trachea can expand to accommodate large prey and can even close during the act of swallowing to prevent food from entering the lungs. A snake can control the trachea’s opening and closing by changing its breathing rate.

Lungs for reptiles vary in complexity from one-chambered lungs to multi-chambered lungs with more surface area. A multi-chambered lung structure is associated with increased pulmonary diffusive capacity for oxygen, but may also increase the likelihood of ventilation-perfusion (V / Q) heterogeneity that restricts gas exchange.

The lungs of a reptile are spongy organs that facilitate gas exchange between blood and the environment. The lungs are surrounded by the ribcage and diaphragm, which protect them from mechanical damage. The lungs contain thin, branching structures that resemble bunches of pink grapes and are labelled as bronchi. These structures connect with the heart, and blood vessels that transport oxygen to and from the lungs are coloured red and blue, identified as arteries and veins.

Tails

Reptiles’ tails are vital for a variety of purposes, including balance, agility and communication. They can also be used as a means of defense and for locomotion. Many species can even regenerate their tails after an injury or to deter predators.

The long, tapered tail of a scorpion serves several functions: it allows the animal to maneuver in the environment, attract and capture prey, and serve as a mating tool during courtship rituals. Equipped with a venomous stinger, the tail also protects the scorpion from potential threats.

In lizards, skinks and snakes the tail helps with locomotion, providing support, enabling acrobatic movements, and serving as a means of defense. Some lizards can detach their tail in a display of aggression or injury to a predator, which distracts the attacker and gives the animal time to escape. The detached tail continues to wriggle for a short period of time, further distracting the predator.

Vibrating the tail is a common defensive behavior seen in many venomous and non-venomous reptiles. For example, when a rattlesnake is disturbed it will vibrate its tail, which creates a sound that can scare off the attacker. Hognose snakes, another venomous reptile, may exhibit this behavior as well. This display is often accompanied by a writhing motion and the release of cloacal fluids. Anatomically, the proximal region of a lizard’s tail will often regenerate after an amputation but distal regions do not re-grow as quickly.